Investigating the journey of an email can be a necessity for a number of reasons. Maybe a sent email never reached its recipient. Perhaps there is reason to believe the content of an email is harmful or malicious, laced with spam or malware. Or it could simply be that we want to break down the journey an email took to get to its destination. Or not get there.
The first thing we need in order to analyze an email’s journey is the message header in full. When we open an email we do not see the full details of that email; just the necessities like name, date, time etc. Without looking at the message header, we can’t really be sure who it’s from, as the name of the sender is often spoofed by spammers. To view a message in full in Gmail for example, hit the ‘See Original’ button in the drop-down menu inside the email you want to analyze.
Whatever your reasons for wanting to decode and investigate an email, here are some tools that will help you find what you’re looking for:
1. Iana.org’s SMTP Enhanced Status Codes Registry
A good place to start when looking into email delivery issues is Iana.org’s SMTP Enhanced Status Codes Registry. By understanding enhanced status codes, we can identify the root cause of why an email delivery failed.
You can find a complete registry of the codes here.
MXToolBox is a tried and trusted source of diagnosis on a range of issues for many IT professionals. The site allows you to diagnose your domain health, analyze message headers and check IPs against over 100 DSN-based email blocklists.
3. G Suite Toolbox Message Header
Get to the root of email delivery issues with G Suite ToolBox’s Message Header. Simply paste the SMTP message header into the box provided and get to the bottom of any email delivery issue. The Message Header tool says it can “identify delivery delays”, "identify approximate source of delay” and “identify who may responsible”.
What if the email issues you are experiencing have nothing to do with content and are not a false positive diagnosis from a spam filter? You can check the status of ESPs such as Gmail, AOL, Yahoo mail and others on DownDetector.
In 2011, Postmark introduced their JSON API which parses outbound and inbound email, "providing easy and fast programmatic usage of SpamAssassin."
The tool works by pasting the message header and contents that you want to rate into the API provided. A spam score is then assigned to the email.
6. Mail Tester
Just as their homepage suggests, Mail Tester tests the ‘spammyness’ of your email. User-friendly and thorough, Mail Tester can lets you know what your spam score is and gives you tips on how you can improve a not-so-great score.